The present invention relates generally to apparatus and method for offshore drilling and more particularly for drilling at great depths.
The drilling for underwater oil deposits situated at places where the water depth is more than 200 meters (6,560 ft) gives rise to considerable technical and economic problems for which no satisfactory solutions have yet been found.
In shallower depths, the conventional approach is to install framework structure derricks whch are driven into the sea bed. The top part of the derrick is above the surface of the water and serves as a support for a working platform containing the drilling equipment, e.g., equipment for pretreating the oil, well-head maintenance and the like.
However, as the depth of the sea increases, the weight of the support structure increases substantially, as do also the difficulties of constructing and installing the structure. Also, as the depth increases, the hydrostatic pressure at the sea bed makes it very difficult to install the well-head units. At these considerable water depths, the sea bed is practically inaccessible. Thus, it is clear that there exists a need for an offshore drilling operation which is capable of being used economically at great depths.